JPH11205630A - Synchronizing separator circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably separate synchronizing while being hardly affected by a noise or the like. SOLUTION: This circuit is provided with a sync chip clamp circuit 10 for clamping the sync chip level of a video signal to a reference voltage Vref, hold circuit 11 for holding the pedestal level of the video signal clamped by the sync chip clamp circuit 10, amplifier 12 for amplifying the video signal clamped by the sync chip clamp circuit 10, and comparator 13 for comparing the level of an output video signal from the amplifier 12 with that of an output voltage from the hold circuit 11, and a horizontal synchronizing signal is led out of the comparator 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronizing separation circuit for separating a horizontal synchronizing signal from a video signal used in a television receiver or a video tape recorder. The present invention relates to a synchronization separation circuit capable of performing synchronization separation.

[0002]

2. Description of the Related Art A sync separation circuit for separating a horizontal sync signal from a video signal used in a television receiver, a video tape recorder, or the like is known. As the sync separation circuit, for example, the one shown in FIG. 2 can be considered. A video signal is applied to the input terminal 1 in FIG. In the applied video signal, the sync tip (the leading end of the horizontal synchronization signal) is clamped by the sync tip clamp circuit 2. The clamp voltage at this time becomes the reference voltage Vref1, which is the voltage of the reference voltage source 3.

[0005] The clamped video signal is applied to a buffer 5 after a noise component is removed by an LPF 4. The video signal that has passed through the buffer 5 is compared in level with a reference voltage Vref2 by a comparator 6. Reference voltage Vref
2 is superimposed on the reference voltage Vref1 and the comparator 6
Is applied to As a result of the comparison by the comparator 6, a horizontal synchronizing signal synchronized with the output terminal 7 is obtained.

[0004]

However, in the method of FIG. 2, when the magnitude of the video signal applied to the input terminal 1 changes, the slicing position changes because the level for slicing the horizontal synchronizing signal is fixed. Oops. When the slicing position changes, it becomes impossible to perform stable synchronization separation.
In extreme cases, synchronization separation itself cannot be performed.

FIG. 3 shows this state. It is assumed that the slicing level approaches the leading end of the horizontal synchronizing signal as shown by a dotted line a in FIG. Then, erroneous determination is likely to occur due to the influence of noise that tends to occur at the tip. Conversely, it is assumed that the level to be sliced approaches the pedestal level as shown by a dotted line b in FIG. Then, as shown in the figure, it is affected by the video signal, and in this case, the erroneous determination is also easy.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has a sync tip clamp circuit for clamping a sync tip level of a video signal to a reference voltage Vref, and a sync tip clamp circuit for clamping the sync tip level of the video signal. A holding circuit for holding the pedestal level of the video signal, an amplifier for amplifying the video signal clamped by the sync tip clamp circuit, and a comparator for comparing the level of the output video signal of the amplifier with the output voltage of the holding circuit. And a horizontal synchronization signal is derived from the comparator.

[0007]

FIG. 1 shows a sync separation circuit according to the present invention. Reference numeral 10 denotes the sync tip level of the video signal as the reference voltage V
sync tip clamp circuit for clamping to ref, 11
Is a holding circuit for holding the pedestal level of the video signal clamped by the sync tip clamp circuit 10; 12 is a differential amplifier to which the video signal clamped by the sync tip clamp circuit 10 and the reference voltage Vref are applied;
3 is a comparator for comparing the level of the output video signal of the differential amplifier 12 with the output voltage of the holding circuit.
PF and 15 are buffers, and 16 is a reference voltage source.

A video signal is applied to the input terminal 17.
In the applied video signal, the sync tip (the leading end of the horizontal synchronization signal) is clamped by the sync tip clamp circuit 10. The clamp voltage at this time becomes the reference voltage Vref which is the voltage of the reference voltage source 16. This is shown in the video signal A of FIG.

The clamped video signal is applied to a buffer 15 after a noise component is removed by an LPF 14. The video signal passing through the buffer 15 is supplied to the differential amplifier 1
At 2, the signal is amplified based on the reference voltage Vref. This is shown in the video signal B of FIG. When the gain of the differential amplifier 12 in FIG. 1 is set to double, the waveform becomes as shown in FIG. 4B.
That is, the amplitude is doubled while the level of the sync chip is kept at the reference voltage Vref.

Therefore, in the present invention, the pedestal level of the video signal A shown in FIG. 4 is detected and used as a slice level so that the slice level comes to the center of the doubled horizontal synchronizing signal. As a result, the horizontal synchronization signal can be separated at an optimum level. In this embodiment, the differential amplifier 1
Although the gain of No. 2 is set to double, it may of course be raised or lowered within an allowable range.

In order to detect the pedestal level of the video signal A shown in FIG. 4, a holding circuit 11 which operates as an S / H circuit (sample and hold) is used. The holding circuit 11
The pedestal level in the video signal passing through the buffer 15 is S / Hed and applied to the comparator 13. As a result, the comparator 13 can slice the horizontal synchronizing signal of the video signal B in FIG.

[0012]

As described above, according to the present invention, the sync tip clamp circuit for clamping the sync tip level of the video signal to the reference voltage Vref, and the pedestal level of the video signal clamped by the sync tip clamp circuit are held. A holding circuit that amplifies the video signal clamped by the sync tip clamp circuit is provided, and the level comparison between the output video signal of the amplifier and the output voltage of the holding circuit is performed. The slice level comes to the center of the signal. If the slicing position is fixed, synchronization and separation can be performed stably regardless of the amplitude of the video signal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a sync separation circuit of the present invention.

FIG. 2 is a block diagram showing a conventional sync separation circuit.

FIG. 3 is a waveform chart for explaining the operation of the related art.

FIG. 4 is a waveform chart for explaining the operation of the present invention.

[Explanation of symbols]

 (10) Sync tip clamp circuit (11) Holding circuit (12) Differential amplifier (13) Comparator (16) Reference voltage source

Claims (4)

[Claims] 1. A sync tip clamp circuit for clamping a sync tip level of a video signal to a reference voltage Vref, a holding circuit for holding a pedestal level of a video signal clamped by the sync tip clamp circuit, and the sync tip clamp circuit An amplifier for amplifying the video signal clamped by the above, and a comparator for comparing the level of the output video signal of the amplifier with the output voltage of the holding circuit, and a horizontal synchronization signal is derived from the comparator. And a sync separation circuit. 2. A sync tip clamp circuit for clamping a sync tip level of a video signal to a reference voltage Vref, a holding circuit for holding a pedestal level of a video signal clamped by the sync tip clamp circuit, and the sync tip clamp circuit An amplifier for amplifying the video signal clamped by the above using a reference voltage Vref, and a comparator for comparing a level between an output video signal of the amplifier and an output voltage of the holding circuit, and derives a horizontal synchronization signal from the comparator A synchronization separation circuit. 3. A sync tip clamp circuit for clamping a sync tip level of a video signal to a reference voltage Vref; a holding circuit for holding a pedestal level of the video signal clamped by the sync tip clamp circuit; An amplifier for amplifying the video signal clamped by the above using a reference voltage Vref, and a comparator for comparing a level between an output video signal of the amplifier and an output voltage of the holding circuit, and derives a horizontal synchronization signal from the comparator A synchronization separation circuit. 4. A sync tip clamp circuit for clamping a sync tip level of a video signal to a reference voltage Vref; a holding circuit for holding a pedestal level of the video signal clamped by the sync tip clamp circuit; A differential amplifier to which a video signal and a reference voltage Vref are applied, and a comparator for comparing a level between an output video signal of the differential amplifier and an output voltage of the holding circuit, and a horizontal synchronization signal from the comparator. A synchronization separation circuit.